The two hot set up's for the XB8 right now for diff's are 3-3-5 or 3-3-3. I personally run 3-3-5.
http://forum.teamxray.com/xform/inde...=544&setup=xb8
That's my set up that I was asked to post by a few of the local racer's. Try it out. It's a fairly agressive set up. The harder you drive the car, the better the set up works.